Soldiers clashed with illegal miners in southern Venezuela on the weekend, killing 18 people in a region notorious for violence and gang rivalries, a lawmaker and local media said.

Bolivar state Governor Justo Noguera said a military unit had fought off an attack, but gave no more details. “An investigation is under way,” he told reporters.

Local newspaper Correo del Caroni reported that 17 men and one woman died in the incident on Saturday morning in an area known for gold and diamond mining.

Echoing that number, a local opposition lawmaker, Americo De Grazia‏, said relatives had described the victims as having bullets in the head. “Massacres are the narco-dictatorship’s state policy,” he said, accusing the security forces.

“Did 18 citizens die and not a single soldier was injured? … They ‘clear’ these gold areas with fire and blood,” said De Grazia

An NGO, the Venezuelan Program of Education Action in Human Rights, tweeted that the operation was “worrisome – a new massacre?”

The government did not respond to requests for comment.

Clashes over illegal mines are common in the remote, mineral-rich area near the border of Guyana, with at least 17 people killed in a gang feud there in 2016.

That year, President Nicolas Maduro declared the area a strategic priority, naming it the Mining Arc and declaring war on the hundreds of illegal miners from Venezuela and neighbouring Brazil who try to make a living there.

Local media said the army captured guns and explosives during Saturday’s operation.